The present invention relates to a timing system for regulating, via respective camshaft-controlled valves, fluid input or output to/from a number of cylinders of an engine and/or machine. In particular, the present invention relates to an overhead camshaft timing system for an internal combustion engine featuring a number of valves, e.g. five, per cylinder.
To improve the volumetric efficiency of internal combustion engines, particularly high-performance engines of sports cars or so-called touring cars, the common design practice is to provide timing systems which, instead of the usual two valves (supply and exhaust) per cylinder, feature for example four (two supply and two exhaust) or five (three supply and two exhaust) valves per cylinder. The latter type in particular involves serious design problems in terms of valve control and/or arrangement of the valves to prevent interference, particularly between the tappets of the three supply valves. To overcome this problem, U.S. Pat. No. 4,615,309 provides for a spread arrangement of the supply valves, the middle one being arranged obliquely in relation to the two lateral valves, thus enabling all three to be controlled by a single camshaft, and for using targets with smaller than normal diameter caps, in the example shown, smaller than the caps on the exhaust valves.
Such a solution, however, still involves a number of drawbacks. Foremost of these is that the small diameter caps, particularly in the presence of valves inclined in relation to the camshaft, and therefore in the presence of possible lateral thrust on the tappets, may result in increased contact pressure between the caps and the cap guides on the cylinder head, thus resulting in impairment of the lubricating oil film and/or greater wear on moving parts.